Cytosolic Ca 2+ regulates a wide range of cell functions, from secretion to metabolism to cell growth and death. It is unknown how Ca 2+ simultaneously controls such diverse activities in an individual cell, although expression of multiple isoforms of the inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R)/Ca 2+ release channel may be responsible by allowing distinct Ca 2+ signals to occur in different subcellular regions. The parent grant for this FIRCA proposal tests the hypothesis that Ca 2+ waves in hepatocytes result from the coordinated release of Ca 2+ from distinct InsP3Rs, and that localized, subcellular increases in Ca 2+ can regulate secretion. The current proposal would complement the hypothesis of the parent grant in an important way, by testing whether distinct isoforms of the InsP3R regulate apoptosis. This question is of fundamental importance in cell biology, since apoptosis contributes to the regulation of cell growth and death in virtually all tissues, and since the InsP3R may be necessary to mediate apoptosis. The specific aims of this project are: 1. To characterize the Ca 2+ signaling machinery in a model epithelial cell line that expresses all three isoforms of the InsP3R. We will examine the expression and subcellular distribution of InsP3Rs and the pattern of InsP3-induced Ca 2+ signals in CHO cells, a model epithelial cell line that expresses all three InsP3R isoforms. 2. To investigate the contribution of each isoform of the InsP3R to the pattern of Ca 2+ signaling. We will determine the contribution of each InsP3R isoform to Ca 2+signaling in CHO cells by selectively inhibiting expression of different combinations of InsP3R isoforms while Ca 2+ signals are monitored by confocal microscopy. 3. To determine the effect of each isoform of the InsP3R on apoptosis. We will examine bile acid-induced apoptosis in CHO cells expressing the bile acid uptake protein NTCP plus different combinations of InsP3R isoforms. This research will be performed primarily at UFMG in Brazil in collaboration with M. Fatima Leite as an extension of NIH R01 DK45710.